Pickling composition



Patented Sept. 30, 1930 .vlvI virvw PATENT orl-"ica HARRY 3. JOHN, OF WASHINGTON, PENNSYLVANIA, ASSIGNOB, BY IESNE ASSIGN- HEN'IS. TO NORMAN A. EMERY, OF YOUNGSTOWN, OHIO rxcxnme conrosirron Io Drawing. Application filed A ril 2,

This invention relates to pickling processes such as are used in the removal of scale from steels and has for its object to reduce the time of pickli and to make it safer and'chea-per. In pick ing steel it is common to heat the acid solution to expedite the chemical action. If this chemical action is further hastened by increase in acid strength it is un-" satisfactory because the stronger acid not only attacks the scale but also the body of metal. If the temperature of the bath is raised too high, evaporation causes waste in acid. Another source of trouble is the release of bubbles of hydrogen, which rise and pass out of the bath carrying particles of acid spray to the injury of exposed metal parts of the building and the workmen. Under this invention these disadvantages are greatly reduced as is also the time of pickling.

Accordingto this invention a substance like alladium sponge having a strong affinity or hydrogen is suspended in the bath. A salt is also added to the bath capable of being acted on to renew theagid and forming a material which inhibits the action of the acid on and protects the body of metal. To lessen loss of acid through vaporization, and assist in acid renewal, a floatable solid or vegetable matter like sawdust or spent tanbark is spread over the surface to cover 1 the bath.

The usual treatment tank and crate for the material being pickled is used.

For treatment of a low carbon cop er nickel steel a 2% to 20% bath of mixed drochloric and nitric acids is used, two parts V a material havi of hydrochloric as one of nitric bein found desirable. About 2% -to 5% by weight of sodium chloride (rock salt) is added and dissolved. Throughout the bath is distributed an aflinity for hydrogen. This is prefers 1y palladium sponge attached to various portions of the crate containin the material to be pickled, as for examp e by means of bronze wire, and about "gallons of t e bath has,

1 lb. of the alladium s nge for each 2,000

11 found satisfactory. After the crated material has been It) placed in the bathe quantity of floatable,

1927. Serial No. 180,627.

solid material like sawdust, spent tanbark, or quebracho bark is spreadv over to cover substantially the entire surface of the bath and lessen vaporization. The bath is preferably heated by live steam to a temperature of 170 to 180 F. On completion. ofthe pickling operation the material is taken out free from scale and immersed in warm rinse water, then in a hot soap solution or otherwise as is customary, to entirely remove the acid from the material. The palladium sponge has a strong afiinity for ydrogen and is ca able of absorbing such a large, quantity of ydrogen that the sponge in usual practice would not ome saturated until in use about a week. Evidence that the palladium sponge has become saturated is seen in the emission of hydrogen from the bath. When saturated the palladium sponge is removed, placed in a crucible and eated to about 800 C. or as low as 500 C. if a vacuum is used, with the result that the lgydrogen is burned out, but no oxidation 0 the spon e occurs at these temperatures. When the ydrog'en has been burned out the palladium sponge is ready to be used over again in the bath. i

The acid used for the bath depends on the kind of materials treated. Where tungsten or chrome steels are treated it has been found desirable to use a mixture of hydrochloric and sulphuric acids. But with agopper or nickel steel the use of hydrochloric and nitric acids is preferred. Commercial sulphuric or hydrochloric acid contains certain im urities such as arsenic and antimony whic ordinarily have an aflinity for the nasent hydrogen, with the result that hydrogen compounds of these materials are precipitated on the metal surfaces in pin spots, which are diflicult to coat with tin, zinc, and the like. The palladium sponge having a stronger aflinity or hydrogenthan the acid impurities, there is no union and preci itation 0 these impurities on the metal sur ace with the result that this surface is cleaner and better adapted for 'sodium chloride is acted upon by the nitric acid to renew the acid and-form sodium nitrate and hydrochloric acid, either directly or by the union of na' sent hydrogen and chloescape of chlorine, any

rine. It is thought the sawdust floating on the surface, beside reducing vaporization, fa.- cilitates acid renewal b precluding the ydrogen not absorbed, and any hydrochloric acid gas coming off from the heated bath. The sawdust also functions to absorb any oil or grease on the bath and thus prevent such from getting on the metal surface. The sodium nitrate formed functions as an inhibitor to lessenacid action on the metal body without unduly reducing its activity'on scale. It is thought that nitric acid, being an oxidizing agent, oxidizes some of the lower oxide scale to higher oxides to render them more susceptible of attack by acid. By reason of the renewal of the acid, a weaker initial acid strength is capable of accomplishing greater results than would the corres onding acid strength which is not renewed. t is thought that palladium facilitates action of the acid on the metal sodium chloride acts as an inhibitor during the formation of the sodium nitrate.

What is claimed is: 1. An acid pickling solution comprising hydrochloric acid, sodiunrchloride, another mineral acid capable of actingon sodium chloride to renew the strength of hydrochloric acid, and particles of solid material floating on the surface of the bath to lessen the escape of gas, thereby enhancing the strength of the hydrochloric acid.

2. An acid pickling bath containing palladium sponge and sawdust spread over to substantiall cover the surface of'the bath.

3. An acid pickling solution containing palladium. V 4. An acid pickling solution containing palladium s onge suspended therein.

5. A picking solution containing a mixture of hydrochloric-and nitric acids and sodium chloride. p

6. A picklin solution containing a 2% to 20% mixture 0% hydrochloric and nitric ac ds with roughlyabout 2% to 5% of sodium chloride, there being a larger amount of nitric than 11 drochloric acid.

.7. A pic ling solution containing about two parts of hydrochloric to one part of nitric acids in the presence of sodium chloride.

8. A'pickling solution containing a mixacid which reacts with sodium chloride and is an oxidizing agent for scale.

In testimony whereof I have hereunto set my hand this 31 day of March, 1927.

HARRY J. JOHN.

pickling solution containing so-. 

